1. Field of the Invention
The invention relates to an optical device utilized for light polarization conversion and more particularly, to a polarization conversion system utilized for LCD/LCoS projectors.
2. Description of the Prior Art
As is widely known, liquid crystal display (LCD) projectors and liquid crystal on silicon (LCoS) projectors commonly convert light sources via a light polarization conversion system to a relatively similar polarization state, such as a P polarization beam or an S polarization beam. Hence, the LCD projectors are also referred to as transmission projectors as they operate by transmitting the light beams through the LCD panels. LCoS projectors on the other hand, operate by reflecting light beams, and thus they are also referred to as reflective projectors.
Please refer to FIG. 1. FIG. 1 is a diagram showing the light polarization conversion system according to the prior art. As shown in FIG. 1, the light polarization conversion system 10 includes a light pipe 12 and a prism module 16 located on the entrance face 14 of the light pipe 12. The prism module 16 includes two triangular prisms 162 and 164 that are positioned at a 90-45-45 degree angle and includes a rhombus prism 166 in between. A polarization beam splitting (PBS) layer 168 is coated on the 45 degree angle face of the triangular prisms 162 and 164. A half-wave plate (HWP) 18 is also located between the entrance face 14 of the light pipe 12 and the rhombus prism 166.
After an unpolarized beam 22 enters through the triangular prism 162, the P polarization beam 24 will pass through the PBS layer 168 and travel directly into the light pipe 12. The S polarization beam 26 on the other hand will first reflect to the 45 degree PBS layer 168 of the triangular prism 164 via the PBS layer 168 and next reflect to the HWP 18. After the S polarization beam passes through the HWP 18, the polarization direction of its electrical field is turned to a 90 degree angle and becomes a P polarization beam 28 and finally enters the light pipe 12. By utilizing this method, the light beams are being polarized linearly to have an equal polarization state and after numerous reflections inside the light pipe 12, uniformized light beams are produced at the exit face of the light pipe 12.